How to hydrate through the heatwave


We look at the science of staying hydrated on long rides with Dr Emma Cockcroft, academic and badass bike racer with Bianchi Dama

If, like us, you’ve found yourself gently perspiring while doing nothing more rigorous than sitting still in a well-ventilated room, the idea of going for a bike ride probably makes all the moisture in your braincells turn to vapour.

Ever keen to find ways to make time on the bike more comfortable, we turn to Dr Emma Cockcroft – bike racer for Bianchi Dama and academic at the University of Exeter – to uncover the formula for battling the heat by keeping your fluids topped up. Here’s a slice of that science.

So Doc, what happens to your body and performance when you get dehydrated while riding?
Water is essential for our bodies to function properly. As little as 2-3% loss in body mass through sweating has been shown to compromise the way our bodies work during prolonged exercise (James et al, 2017). 

That’s because dehydration leads to increased core temperature, reduced blood volume and an increase in the rate at which we use muscle carbohydrate stores, which essentially leads to performing at a sub-optimum level with significantly slower time trial performance and power output. 

It also leads to increased rates of perceived exertion. In other words, you feel hotter, your ability to get oxygen to you muscles reduces, you rely more on carbohydrates and it all feels that bit harder.

So, how should riders try to stay hydrated on long rides – especially in hot weather like this?
First, make sure you start your ride hydrated. If you’ve been on the beers the night before you’ll be starting on the back foot. Think about hydration as soon as you get up. 

Don’t wait until you start to suffer and make sure you keep on top of hydration as soon as you start to ride. 

How much you need will depend on how much you sweat (your sweat rate). You can work this out by weighing yourself before and after a ride and seeing how much fluid you’ve lost. 1kg weight loss after an hour = 1 litre of fluid. As a guide, you should aim to drink 1/litre per hour (although this will vary depending on conditions).

Is it just water you need to keep topped up on?
When you sweat you don’t just lose water, but also electrolytes, which are are essential for fast rehydration and good muscle function. On long distance cycles, electrolyte depletion can impair performance, so it’s important you replenish electrolytes as well as water when you ride.

You should also make sure you continue hydrating after a ride too. The need for fluids isn’t over just because you’ve stopped exercising.

Is good old H2O the best thing to be supping on a long hot day in the saddle?
Maughan et al, 2015, looked at the hydrating effects of lots of different drinks compared to still water. 

They found that skimmed milk and – unsurprisingly – oral rehydration solution were the best performing liquids for rehydration. ‘Sports drink’ barely registered a higher rehydration index than regular water, while coffee appeared to actually rehydrate your body worse than water. 


Thanks Doctor Emma! Here's the science in a bullet-pointed nutshell...

  • Drink a lot before you go out riding, instead of waiting to get thirsty

  • Have a couple of sachets of Dioralyte in your jersey for shaking out into your bidons when things get really toasty

  • Don’t drink a whole bottle of Aperol the night before you have a big ride planned.

Follow these wise words and you should find riding in high heat is not only easier, but actually downright enjoyable from start to finish.

See Doctor Emma in action here

tan doan